Using an ATX PSU

I tried using an ATX PSU to power an arduino this evening.

I've got a PSU tester where you plug the main power header (that normally goes in the mobo) into it and it fires up the PSU and has a series of indicators for whether it's good or not. It runs fine on that, all lights are green.

I've had a google and found out I need to connect the green wire to ground (short pins 14 and 15 - I think. I've closed the relevant window put it's the green one with a black one next to it).

However, when I do this, the PSU goes for a few seconds then turns off again. I tried it with the arduino plugged into it, same thing happened.

What have I missed?

sometimes shorting green to ground will work, most of the times you need some form of load on the psu to keep it on

I have seen people use a fairly hefty wattage, low ohm ceramic/sand resistor mounted on a heatsink


quote from the article

ATX power supplys have a minimum load which should be listed on the power supply. Mine requires .3A on the 3.3v line, 1A on the 5v line, and 1A on the 12v line.

which is also why those power supply testers also come with a warning to not leave them on for long periods of time

Thanks osgeld. The PSU doesn't say what the load needs to be, I'll try the load you quoted.

yea I am sure any of mine does not either, but I have seen them on some early (read p2 p3 era) 250 watt supplies

when it came for me to use a computer psu, I had a couple AT models laying around so no issues there

Try to connnect one or two fans to the PSU, some models dont like to work unloaded.

You may be interested in this link:

They do not say anything about having to have a load on the PSU. It would seem, from what Osgeld says, that this product will not work?

read that product's comments, its in debate

personally, not disclosing the possibility of it not working due to common knoledge is irresponsible and almost dishonest of sparkfun, but I know they dont care, as their site is full of "screw you's" and "gotchas"

I tried another spare PSU, and it works fine without a load.

There's no indication on either PSU of this fact, but I suppose it's not relevant to its normal use so it's a bit of a lucky dip.